Is one who prays Tarawih and leaves after eight rak'ahs, or before the Imam who prays twenty-one rak'ahs departs, considered to have observed qiyam al-layl, taking into account the hadith, "Whoever prays with the Imam until he departs, it is recorded for him that he observed qiyam al-layl"?

The hadith which states that whoever prays with the Imam until he departs will have the reward of a night's prayer written for him means that he will attain the reward of a complete night's prayer. If the worshiper leaves before the Imam, he will be rewarded for the portion he prayed, and his faith will not be lost. However, he will miss out on the reward of the entire night's prayer, which is obtained by staying with the Imam until he departs. It is better to stay with the Imam to attain the great reward if one has the ability and time. If one leaves before the Imam, there is no sin upon him, and he will be rewarded for the portion he prayed. Sheikh Al-Uthaymeen preferred the view that the two Imams in Tarawih prayer are like a single Imam.